[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at 17cec6a Revert 1c021c64c "[SCEV] Model ptrtoint(SCEVUnknown) cast not as unknown, but as zext/trunc/self of SCEVUnknown"
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   17cec6a..f180057  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to f1800579666c80adf8bb2f992a639e5b8e3a389b.
CMake Error at CMakeLists.txt:3 (cmake_minimum_required):
  CMake 3.13.4 or higher is required.  You are running version 3.7.1


-- Configuring incomplete, errors occurred!